It is a well-known concept to employ a toothed wheel or gear having equiangularly spaced teeth on the engine crankshaft or camshaft in conjunction with a fixed sensor to provide a pulse train output signal as the toothed wheel rotates. The pulse train signal is used to provide information about the speed of the engine. In addition, angular position may also be determined by way of analyzing the pulse train signal to provide information with regard to a specific position or tooth which has just passed the sensor. The timing information which is derived therefrom is useful in controlling ignition timing as well as timing and fueling of fuel injection systems.
Numerous patented methods and devices are known for detecting engine position and speed. Cockerham, U.S. Pat. No. 4,797,827, discloses an angular position detector which includes a toothed wheel with a missing tooth and a single sensor providing a pulse train signal corresponding to the teeth of the wheel passing nearby. A missing tooth is used to determine engine position. Other patents incorporating the missing tooth technique for determining engine position include Karle et al., U.S. Pat. No. 4,982,330; Capurka, U.S. Pat. No. 4,553,426; and Nakamura et al., U.S. Pat. No. 4,825,373. Further, Kumagai, U.S. Pat. No. 4,870,587, combines the missing tooth detection scheme with the fact that the rotational speed of the crankshaft or camshaft after top dead center of a cylinder rises substantially relative to engine speed before top dead center in a compression stroke of the cylinder but does not rise in an exhaust stroke. Thus, the stroke of the engine is discriminated by determining the difference in rotational speed of the crankshaft before and after top dead center of a cylinder.
Another approach well-known in the art for detecting engine position and/or speed is to provide a toothed wheel wherein one of the teeth is altered slightly in shape or phase relationship with regard to the remaining gear teeth to produce an identifiable position signal thereby indicating relative position of the camshaft or crankshaft of the engine. Specifically, Lotterbach et al., U.S. Pat. No. 4,700,305, discloses a device for controlling a vehicle engine computer using a segmental disk transducer for indicating a specific marker angular position of the crankshaft. The segmented disk includes uniformly spaced segments thereon wherein the number of segments corresponds to the number of cylinders. One of the segments is foreshortened, so that the passage of the leading flank thereof past a stationary pick-up transducer will occur at a time later than that of the leading edges or flanks of the remaining segments. Deutsch, U.S. Pat. No. 4,941,445, discloses an electronic position sensor assembly and engine control system wherein two sensing elements in a dual sensor provide separate and independent position signals related to a multi-cylinder engine cycle position. Reference signals for determining engine position are generated in accordance with several extra-large teeth located on a rotating toothed wheel. Akasu, U.S. Pat. No. 4,959,996, discloses a control signal generator for an internal combustion engine. The toothed wheel disclosed in Akasu is substantially similar to that shown in Lotterbach et al.
Other prior art concepts for determining position and speed of an internal combustion engine are disclosed in Normura et al., U.S. Pat. No. 4,972,818, and Beyer et al., U.S. Pat. No. 4,889,094. Normura et al. discloses a toothed wheel having several missing teeth and phase shifted teeth whereas Beyer et al. discloses a toothed wheel having one tooth which is not notched or split to provide a special timing position signal.
Systems which incorporate the missing tooth approach rely upon detection of the remaining teeth in order to establish the approximate position of the missing tooth for timing purposes. Such an approach will at times produce undesirable timing results during acceleration or deceleration of the engine when the timed projected occurrence of the missing tooth must be estimated by the engine control system.
A more reliable and highly accurate position and speed sensor for use with an internal combustion engine is needed.